Systems and methods for digestion of solid waste

ABSTRACT

This invention relates generally to systems and methods for digestion of solid waste that simplify solids handling. In certain embodiments, anaerobic methane extraction takes place for a period of time (e.g., from 1 to 4 weeks), after which an aerobic composting process begins in the same chamber. The organic waste remains in place and oxygen (e.g., in air) is forced into the chamber for an additional period of time (e.g., from 2 to 4 weeks). At the conclusion of the aerobic phase, the process yields a rough compost product that is stable and pathogen free. The rough compost can be further processed and blended to create high value engineered soils.

RELATED APPLICATION

This application is a continuation application of U.S. patentapplication Ser. No. 13/444,140, filed Apr. 11, 2012, which granted onJul. 23, 2013 as U.S. Pat. No. 8,492,134, which is a continuationapplication of U.S. patent application Ser. No. 13/226,006, filed Sep.6, 2011, which granted on Dec. 11, 2012 as U.S. Pat. No. 8,329,455,which claims priority to and the benefit of U.S. provisional patentapplication Ser. No. 61/505,696, filed Jul. 8, 2011, the disclosures ofwhich are hereby incorporated by reference herein in their entireties.

FIELD OF THE INVENTION

This invention relates generally to the digestion of solid waste. Moreparticularly, in certain embodiments, the invention relates to apparatusand methods for decomposing organic matter into biogas and compost.

BACKGROUND OF THE INVENTION

The degradation of organic matter is a process that occurs aerobicallyand/or anaerobically in nature by the complex interaction of a multitudeof microorganisms. Controlled more or less industrialized methods havebeen known for a long time and referred to as composting for aerobicprocesses and fermentation, bio-methanisation, or simply anaerobicdigestion (AD), for the anaerobic processes. AD processes may be dividedinto two principle steps: hydrolysis and methanogenesis.

The two processes of composting and AD have been developingindependently over the last many years. Composting as a way to producecompost for fertilization and soil improvement has been thoroughlydescribed many places. Likewise, one-stage, two-stage, or multi-stage ADmethods have been developed on the basis of the most varieddevelopments. In addition to wet AD developed from liquid-manure andwastewater treatment, dry AD is also practiced.

The principle of the two-step, two-stage AD was described for the firsttime by Ghosh in 1978. In this process, wastes are percolated in ananaerobic reactor. The percolation water is subsequently fermented tobiogas in a methane reactor. The method was further developed andpatented by Rijkens and Hofank (U.S. Pat. No. 4,400,195) in the 1980sfor organic wastes. The method was converted twice to practice, to theANM method in Ganderkesee and to the Prethane-Rudad method in Breda.Tests were conducted by Wellinger and Suter in the 1980s with solidmanure, and by Widmer with market and meatpacking wastes. In the lattercase, the percolator was also driven in an aerobic environment.

The newest plants, which have been developed according to this method(for residual wastes) are the ISKA® percolation method in Sansenheck,and the BIOPERCOLAT® method (DE 198 46336 A1). Here, the waste ishydrolyzed in a percolator after a mechanical pretreatment (for example,sieving, metal separation). The percolator is therefore equipped with astirring mechanism, so that the wastes are continually transportedthrough the reactor. After a residence time of 2 to 3 days, thepercolate is discharged free of water and ready for further treatment ordepositing in a layer. The percolation water is fermented anaerobicallyto biogas in a methane reactor after separation of sand and fibers. Thewater that is cleaned in this way is directly used as percolation wateror is used after another cleaning (e.g., for removing nitrogen).

Large amounts of organic solid wastes are produced in many towns andcities all over the world, and treatment methods are often limited bysolids handling requirements for adequate sterilization of these largeamounts of heavy, solid waste. Accordingly, there is a need for improvedsystems and methods for digestion and composting of solid wastes withlimited solids handling requirements.

SUMMARY OF THE INVENTION

A system is presented for solid waste treatment that does not requiremoving the solid fraction of the waste between different stages of theprocess. Only initial loading of the waste and final unloading of thesolids after sanitization is needed.

In one embodiment, organic waste is loaded into a chamber that resemblesa garage. After filling, the door is closed and anaerobic conditions arecreated. Anaerobic methane extraction takes place for a period of time(e.g., from 1 to 4 weeks), after which an aerobic composting processbegins in the same chamber. The organic waste remains in place andoxygen (e.g., in air) is forced into the chamber for an additionalperiod of time (e.g., from 2 to 4 weeks). At the conclusion of theaerobic composting phase, the process yields a rough compost productthat is stable and pathogen free. The rough compost can be furtherprocessed and blended to create high value engineered soils. There is norequirement to handle raw, post-methane extraction digestate prior tocomposting. The biogas produced has a high methane content, e.g., about70% or more, compared to about 55-60% using other processes. The biogasalso has lower concentrations of VOC's, siloxane, and othercontaminants.

The system employs dry anaerobic digestion in which bacterialhydrolysis—that is, the leaching out of fatty acids from the organicsolid waste—is physically separated from methane generation. A series ofhydrolysis and methane generation (gasification) stages are conductedfor a period of time (e.g., from 1 to 4 weeks) under anaerobicconditions with the solid waste in a waste processing tank operating atambient (e.g., atmospheric) pressure. Percolate liquid is recirculatedthrough a grating at or near the base of the waste processing tankduring the hydrolysis stage. The percolate is pumped into a biogasreactor tank in which methane and/or other biogases are produced, thenfiltered, degassed percolate is pumped back to the waste processingtank. After hydrolysis and gasification is completed, the wasteprocessing tank becomes a composter, such that air flows through thesolid waste, through the grating at the base, then passes through abiofilter before being released into the atmosphere. After composting,the solid waste is sufficiently sanitary for removal and may be safelydisposed or used as a byproduct.

During all three stages—hydrolysis, gasification, and composting—thewaste processing tank remains closed. No solid waste is moved, and onlyfluids and air circulates between the process module and the gas reactorin a closed system. The system design insures that the processes ofhydrolysis, percolation, methane generation, and composting are separateand occur rapidly and efficiently. There is no need for inoculationusing earlier processed material to start fresh batches, therebyinsuring full traceability of the waste. The process is self-sustainingand there is no need for heating to start the process, allowing for ahigh energy efficiency. A wide variety of organic waste types may beprocessed, for example, municipal waste; industrial, commercial, andinstitutional waste; garden waste; and sewage sludge.

Thus, in one aspect, the invention relates to a system for decompositionof organic matter into biogas and compost, the system including: a wasteprocessing tank into which solid organic waste is loaded and in whichhydrolysis and composting takes place at separate times, with compostingof the solid organic waste taking place during a separate stage afterhydrolysis is completed, wherein the waste processing tank comprises adrain at or near its base, the drain allowing flow of percolation liquidout of the waste processing tank during the hydrolysis stage, the drainalso serving as a vent through which air flows into and/or out of thesolid organic waste in the waste processing tank during the compostingstage; a spraying system configured to spray percolate liquid onto thesolid organic waste in the waste processing tank during the hydrolysisstage, wherein the percolate liquid comprises fatty acids leached fromthe solid organic waste and wherein the percolate liquid is recycledfrom the base of the waste processing tank during the hydrolysis stage;and a biogas reactor tank into which the percolate liquid from the wasteprocessing tank is pumped for generation of biogas under anaerobicconditions during a gasification stage. In certain embodiments, thewaste processing tank is configured to operate at ambient pressureduring the hydrolysis stage, the composting stage, or both. In preferredembodiments, the waste processing tank is configured to operate underanaerobic conditions during the hydrolysis stage.

In certain embodiments, the system further includes a biofilter throughwhich air from the waste processing tank passes prior to discharge tothe atmosphere during the composting stage. In certain embodiments, thesystem further includes a filter configured to separate solids from thepercolate liquid.

In certain embodiments, the system includes at least two wasteprocessing tanks connected in parallel. In certain embodiments, thewaste processing tank includes an acid-resistant lining or coating. Thebiogas reactor tank is preferably gas-tight. The system may also includea heater for heating the percolate liquid either in the biogas reactortank or outside the biogas reactor tank (for later introduction backinto the tank after heating). In certain embodiments, the biogas reactortank includes a sump to separate sediment and/or particles from thepercolate liquid.

In preferred embodiments, the system further includes a liquid processtank into which percolate liquid from either the biogas reactor tank,the waste processing tank, or both flows prior to being pumped to thespraying system for spraying onto the solid organic waste in the wasteprocessing tank during the hydrolysis stage. In certain embodiments,there is one liquid process tank for every waste processing tank. Incertain embodiments, there is at least five waste processing tanks(e.g., each with their own associated liquid process tank), for everybiogas reactor tank (there may be one or more biogas reactor tanks inthe system). In certain embodiments, percolate liquid from both thebiogas reactor and the waste processing tank flows into the liquidprocess tank prior to being pumped to the spraying system for sprayingonto the solid organic waste in the waste processing tank during thehydrolysis stage. The system may further include a filter tankconfigured to separate solids from the percolate liquid before thepercolate liquid enters the liquid process tank.

Elements of other aspects of the invention can be applied to this aspectof the invention as well.

In another aspect, the invention relates to a method for decompositionof organic matter into biogas and compost, the method including thesteps of: (a) loading solid organic waste into a waste processing tank;(b) during one or more series of hydrolysis and gasification stages: (i)spraying percolation liquid over the solid organic waste in the wasteprocessing tank during a first (and/or subsequent) hydrolysis stage inwhich bacterial hydrolysis takes place; (ii) optionally recirculatingthe percolation liquid after it passes through the solid organic wastein the waste processing tank during the first (and/or subsequent)hydrolysis stage; (iii) pumping percolation liquid into a biogas reactortank for generation of biogas during a first (and/or subsequent)gasification stage; (iv) pumping percolate liquid out of the biogasreactor tank following the first (and/or subsequent) gasification stage,for spraying over the solid organic waste in the waste processing tankduring a second and/or subsequent hydrolysis stage; and (c) followingall hydrolysis and gasification stages, ventilating the waste processingtank for composting of the solid organic waste under aerobic conditions.

In certain embodiments, the series of hydrolysis and gasification stagesis carried out for a period of from 1 to 4 weeks (e.g., for about 21days) before the composting stage begins. In certain embodiments,methanogenesis takes place in the biogas reactor tank during thegasification stage. In preferred embodiments, the hydrolysis andgasification stages take place under anaerobic conditions. In certainembodiments the one or more hydrolysis stages (and/or the gasificationstage(s)) take place under atmospheric pressure. Hydrolysis generallytakes place at the same time as gasification, but the processes occur indifferent tanks.

In certain embodiments, the percolation liquid is passed through afilter tank configured to separate solids from the percolate liquid,then the filtered liquid is transported into a liquid process tank whereit mixes with liquid from the biogas reactor tank before beingrecirculated via spraying over the solid organic waste in the wasteprocessing tank. In certain embodiments, the percolation liquid enters aprocess tank where it mixes with liquid from the biogas reactor tankbefore being recirculated via spraying over the solid organic waste inthe waste processing tank.

In certain embodiments, the method comprises flooding the wasteprocessing tank with percolation liquid at least once during thehydrolysis stage.

In certain embodiments, the temperature of the organic solid waste inthe waste processing tank reaches at least 60° C. during at least partof the composting stage. In preferred embodiments, the method furtherincludes the step of passing air through a biofilter after it has passedthrough the solid organic waste in the waste processing tank during thecomposting stage. In certain embodiments, the solid organic waste in thewaste processing tank has been sanitized by the end of the compostingstage.

The description of elements of the embodiments above can be applied tothis aspect of the invention as well.

In another aspect, the invention relates to a dual-purpose drainassembly for transport of percolate from a process module during adigestion stage and for ventilation of the process module during acomposting stage of a waste processing system, the drain assemblyincluding one or more rails through which a plurality of conduits aredrilled, wherein each of the conduits has (i) a first end facing theprocess module containing solid waste being processed and (ii) a secondend facing a pipe through which liquid percolate flows out of theprocess module during hydrolysis and through which air flows into theprocess module during composting, wherein the first end has a width ordiameter smaller than the second end's. In certain embodiments, thefirst end has a diameter (or width) no greater than 90% of that of thesecond end. In certain embodiments, the ratio of the diameter of thefirst end to the diameter of the second end is about 0.75.

In certain embodiments, each of the rails has a notch, and two or moreof such notched rails form a shelf for supporting a removable plate(e.g., stainless steel plate) that prevents the solid waste in the wasteprocessing module from entering the pipe. In certain embodiments, thepipe is a conduit formed in a concrete base below the process module.

Elements of other aspects of the invention can be applied to this aspectof the invention as well.

BRIEF DESCRIPTION OF THE DRAWINGS

The objects and features of the invention can be better understood withreference to the drawings described below, and the claims. The drawingsare not necessarily to scale, emphasis instead generally being placedupon illustrating the principles of the invention. In the drawings, likenumerals are used to indicate like parts throughout the various views.

While the invention is particularly shown and described herein withreference to specific examples and specific embodiments, it should beunderstood by those skilled in the art that various changes in form anddetail may be made therein without departing from the spirit and scopeof the invention.

FIG. 1 is a schematic drawing of an apparatus for digestion andcomposting of solid waste, highlighting components involved in thehydrolysis and methanogenesis stages, in accordance with an embodimentof the invention.

FIG. 2 is a schematic drawing of an apparatus for digestion andcomposting of solid waste, highlighting components involved in thecomposting stage, in accordance with an embodiment of the invention.

FIG. 3 is a schematic drawing of an apparatus for digestion andcomposting of solid waste, highlighting components involved in thehydrolysis and methanogenesis stages, in accordance with an embodimentof the invention.

FIG. 4 is a schematic drawing of an apparatus for digestion andcomposting of solid waste, highlighting components involved in thecomposting stage, in accordance with an embodiment of the invention.

FIG. 5 is a schematic drawing of views of a dual-purpose drain assemblyfor transport of percolate from a process module during a digestionstage as well as for ventilation of the process module during acomposting stage, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

It is contemplated that apparatus, devices, systems, methods, andprocesses of the claimed invention encompass variations and adaptationsdeveloped using information from the embodiments described herein.Adaptation and/or modification of the devices, systems, methods, andprocesses described herein may be performed by those of ordinary skillin the relevant art.

Throughout the description, where apparatus, devices and systems aredescribed as having, including, or comprising specific components, orwhere processes and methods are described as having, including, orcomprising specific steps, it is contemplated that, additionally, thereare apparatus, devices and systems of the present invention that consistessentially of, or consist of, the recited components, and that thereare processes and methods according to the present invention thatconsist essentially of, or consist of, the recited processing steps.

It should be understood that the order of steps or order for performingcertain actions is immaterial so long as the invention remains operable.Moreover, two or more steps or actions may be conducted simultaneously.

It is contemplated that methods, systems, and processes of the claimedinvention encompass scale-ups, variations, and adaptations developedusing information from the embodiments described herein. The processesand methods described herein may be performed using reactor equipmentthat is known to those of ordinary skill in the art, including, withoutlimitation, for example, batch reactors, plug-flow reactors,continuously-stirred tank reactors, packed-bed reactors, slurryreactors, fluidized bed reactors, and columns. The processes describedherein may be conducted in batch, semi-continuous, and/or continuousoperation, or adapted therefor. It is also contemplated that methods,systems, and processes of the claimed invention may include pumps, heatexchangers, and gas-, liquid-, and/or solid-phase material handlingequipment known to those of ordinary skill in the art.

The mention herein of any publication, for example, in the Backgroundsection, is not an admission that the publication serves as prior artwith respect to any of the claims presented herein. The Backgroundsection is presented for purposes of clarity and is not meant as adescription of prior art with respect to any claim.

In certain embodiments, the invention relates to a method for convertingorganic matter into biogas and compost. The organic matter may be sortedand mixed with green structure, introduced in a process module, wherepercolate, recycled in a process tank, washes out nutrients (e.g.,volatile fatty acids). Excess percolate may be pumped through a coarsefilter to a reactor tank where the anaerobic digestion takes place.Biogas produced in the reactor tanks may be transported to utilization.Degassed percolate may then be returned to the process tank for washingout additional nutrients from the organic matter.

In another embodiment, after a period of time, and when the pH reaches aspecified value, the percolation process is stopped, an air-intake isopened, and through the drain system, used for percolation, air is drawnthrough the organic matter to initiate the composting process. Aftercompositing, the process modules are emptied, and the material is leftin open bays for after maturation, until it is sorted and the final soilimprovement products ready for market.

In certain embodiments, the two-stages (AD and composting) are combinedwith a time-dependent and physical split of the AD process in hydrolysisand methanogenesis. For example, in a first process cycle, percolationof dry organic matter causes hydrolytes (such as volatile fatty acids,etc.) to be extracted, and the percolate (the wet fraction) is deliveredto a biogas reactor tank for methanogenesis. In one embodiment, thehydrolysis takes place under anaerobic conditions. Hydrolysis may beaccomplished in the solid phase, followed by methanogenesis in the wetphase, followed by methanogenesis in the solid phase, and finallycomposting of the dry phase.

In certain embodiments, AD and composting are achieved using specializedprocess modules (PM) and a methane reactor (MR). In one embodiment, amixture of structure and organic matter is loaded into the PMs, and oneor more gates to the PMs are closed. Run off (i.e., percolate)containing hydrolytes from the PM may be delivered to a process tank(PT) prior to transfer to the MR.

In certain embodiments, degassed liquid from the MR is returned to thePT, from which it may be sprayed onto the organic matter in the PM. Thepercolate from the PM may be fed back to the process tank, through adrain in the bottom of the PM. In one embodiment, the process module isoperated under anaerobic conditions during percolation. Excesspercolation liquid, now containing hydrolytes, may be fed through acoarse filter, and introduced into the MR, where the methanogenesistakes place. Separation of fresh and degassed percolate may take placeusing a principle of leveling in the reactor tank. Percolate may becontinuously taken out of the MR and heated in a heat exchanger.

When the pH of percolate coming out of the process module has reached adefined level, and the solid fraction in the PM has been inoculated bymethanogenic bacteria, the methanogenesis may start in the PM. After aperiod of time, the methane production or accumulation in the PM isstopped. In one embodiment, for example, an air intake is opened and afan starts to draw air (including oxygen) through the organic matterstill contained and enclosed in the process modules. During this portionof the process, when composting takes place, the process module isoperated under aerobic conditions. In another embodiment, the air isintroduced or extracted through the same drain as that the percolationfluid passes through during percolation.

The introduction of air may start a composting process of the organicmatter in the process modules. In certain embodiments, this causes thetemperature to increase, and a sanitization process will take place.Further, water may evaporate from the organic matter, thereby reducingthe moisture content. After leaving the organic matter, the air may befed through a biofilter and an optional scrubber for elimination ofodors.

In certain embodiments, when the temperature of the organic matter inthe process module has reached a defined level, or the compostingprocess has taken place for a specific period of time, the fan isstopped. At this point, a door or gate the process module may be opened,and the degassed and composted organic matter may be taken out of theprocess module. The organic matter may then be left outside in open baysfor after maturation, before final screening and mixing for compost orsoil improvement products.

In certain embodiments, a decomposing method for organic matter isprovided in which an amount of biogas is formed according to need. Ananaerobically driven process module may be loaded with a mixture ofstructure and organic matter. In one embodiment, a percolation liquid issprayed onto the organic matter, led through the bottom of the processmodule to a process tank, from where is again sprayed on the organicmatter. In another embodiment, excess percolation liquid is passedthrough a coarse filter into a reactor tank, where it is fermented tobiogas. The degassed percolate may be fed back to the process tank.

The decomposing methods described herein are advantageously based on asimple and robust process. In this way, control of the biogas formedaccording to need is made possible, and a biogas requirement, forexample, for conversion to electrical energy or production of heat atpeak times or times of low demand, can be controlled accordingly. Whilecontrol of biogas production may not be provided or may be provided onlyin constricted periods for adapting to consumption in known plants, arapid adaptation to the current requirement can be provided with thedecomposing method, in accordance with an embodiment of the invention.

All substances originating from living organisms may be considered to bebiogenic materials, including, in particular, the following: bio-wastes,lawn cuttings, curbside clippings, garden clippings, bio-solids,industrial waste, food waste, household waste, agricultural waste,kitchen waste, renewable resources, and similar materials.

Since, in certain embodiments, hydrolysis and methanogenesis arephysically and time-wise separated, the biogas contains lowconcentration of sulphur, and silicas, thus cleaning of H₂S and SiO_(x)is not necessary when applying the biogas for heat and power productionin an IC engine.

In one embodiment of the invention, the construction of the bottom ofthe process module, used for percolate discharge and air exhaust, isperformed in a manner so blocking does not occur. In this way, thedesign may ensure that percolate and air always have free passage duringoperation.

As mentioned, in certain embodiments, the atmosphere is anaerobic duringpercolation and aerobic during composting. It is further possible toinsulate or even heat the PMs. For example, the temperature in theprocess module may be approximately 38° C. under percolation and 70° C.during composting.

In certain embodiments, all of the liquid in the system is pumpedthrough one circuit. The percolation liquid leaving the reactor tank, asdegassed percolate, may be discharged discontinuously and replaced withfresh, hydrolyte rich liquid. In this way, a concentration of foreignmatter in the circuit may be avoided. In another embodiment, substancesthat sink and/or float are separated in the reactor tank in a sump,equipped with a pump that is able to remove sludge.

In certain embodiments, methanogenesis of the percolate to biogas isconducted by means of bacteria. In this case, the methanogenesis may beconducted with the participation of a bacterial matrix of severalbacterial strains. The methane reactor can be heated; for example, itcan be heated by taking out a slipstream of liquid and heating theliquid in a heat-exchanger before it is introduced again into thereactor tank. In this way, a constant temperature can be maintained inthe biogas reactor. The temperature within the biogas reactor may be,for example, between about 38° C. or 55° C.

In addition, in certain embodiments, the an apparatus is provided thatincludes at least one process module, a process tank, a filter tank, anda reactor tank. The process module may be equipped with at least onepump and one fan. The methane reactor tank can be, for example, CSTR,UASB, or another type for AD. Compared previous systems, because theprocess step of methanogenesis occurs in the MR, overfeeding is muchless likely to occur and it is easier to control and/or measure.

Preferably, in one embodiment, the biogas plant includes at least fiveparallel-connected process modules. In this case, the percolation liquidmay be sprayed continuously or discontinuously over the organic matter.Spraying may be performed by a separate pump for each process modulethrough a specially designed spraying system, depending on the materialused. For example, a separately operable liquid circuit may be formedfor each process module. A connection between one or more individualpercolators may be used to inoculate the organic matter with specificspecies of bacteria.

The use of at least two percolators, in some embodiments, has theadvantage that a loading and unloading of solid materials is possible atany given time. In addition, the substrate specific residence time ineach process module can be controlled individually.

Due to acids that may be formed during the decomposition process, theprocess modules are preferably acid-resistant. In certain embodiments,the percolation liquid dissolves the acids and/or other materials thatform, and/or the percolation liquid is enriched with hydrolytes that canbe easily transformed to methane.

In one embodiment, the process modules have a special designed bottom.During percolation, the bottom of the process modules is used to performa solid-liquid separation, where the separated percolation liquidcollects under the drain and is sprayed continuously or discontinuouslyin the circuit over the organic matter by means of pumps. Excesspercolation liquid may be pumped into the buffer tank with appropriatefilling level, and from there into the biogas process reactor. Duringcomposting, the bottom of the process tanks may be used for airdischarge, after the air has passed through the organic matter. Thetemperature in the process modules may be approximately 38° C. Theprocess modules may be insulated and/or heated.

In certain embodiments, the AD is provided by means of added and/orimmobilized bacteria, which are continuously prevailing and produced inthe methane reactor. The methane reactor tank may be essentiallygas-tight and/or may function according to a reactor principle that iscommon to wastewater technology. For example, the reactor tank may be anUp-flow Anaerobic Sludge Bed (UASB-sludge bed), a solid bed reactor,and/or a Continuously Stirred Tank Reactor (CSTR). A solid bed biogasreactor tank can be, for example, operated as a plug flow reactor, sothat both the residence time in the process module as well as theresidence time in the biogas reactor tank can be defined and controlled.

In certain embodiments, the biogas includes methane (CH₄) [e.g., 50-85vol. %], carbon dioxide (CO₂) [e.g., 15-50 vol. %], as well as oxygen,nitrogen, and trace gases (including hydrogen sulfide). A biogas with ahigh methane fraction of between about 65 and about 80 vol. %, or more,may be produced with the decomposing method according to the invention.

Among other things, the biogas can be used directly for heating purposesor, by means of a block-type thermal power system (IC engine, Fuel Cell,Turbine), for the coupled production of electricity and heat, or it canbe upgraded for introduction in pipeline systems or used for vehiclefuel. In various embodiments, the gas is produced by anaerobic digestionof organic matter.

To increase the biogas yield, co-materials (for example, renewableresources or wastes from the food industry) can be used. The AD andcomposted organic matter can subsequently be evaluated as high-valuefertilizer for agricultural use.

In certain embodiments, during the methanogenesis, a slipstream of thepercolate leaves the reactor tank, is heated in a heat exchanger orother heating device, before being reintroduced in the reactor tank. Inthis way, a constant temperature can be maintained in the biogas reactortank. The temperature in the biogas reactor tank may be between about38° C. and about 55° C. In certain embodiments, the temperature in thebiogas reactor tank is about 38° C., or about 55° C.

An accumulation of the most varied substances in the percolate can beavoided, as a mechanism in the bottom of the reactor tank (e.g., a sump)allows particles to be continuously or frequently removed from theprocess.

FIG. 1 depicts an apparatus 20 for digestion of solid waste, inaccordance with an embodiment of the invention. In one embodiment, theprocess tank 1 operates at ambient pressure. Liquid percolates throughorganic matter in the process tank 1 and exits through a draining system(a grating) 3 at the bottom. The percolate is collected in a processtank 5, then pumped to a spraying system 2 back into the process tank 1with a pump 4. Excess percolation liquid is pumped into a filter tank 6by another pump 8, where it is filtered, then is pumped into a biogasreactor tank 9. Degassed percolation liquid is discharged from thebiogas reactor tank 9 and returned to the process tank 5.

Process modules 1 are constructed as a type of “garage” or container,with an acid-resistant lining. The process modules 1 are configured suchthat they are charged by the usual technological means (for example,with wheel loaders). A bottom of the process modules 1 includes a drainsystem 3 so that a solid-liquid separation can occur. The drain system 3is designed and constructed to prevent blocking or clogging. The processmodules 1 may operate at ambient pressure.

The percolation liquid is drained or percolated through organic matterand exits the process modules 1 through the draining system 3 at thebottom of the process modules 1. The percolate is collected in processtanks 5, from which it is pumped to a spraying system 2 in the processmodules 1. The spraying system 2 continuously or discontinuously spraysthe liquid over the organic matter in the process modules 1 by means ofpumps 4.

During operation of the apparatus 20, the percolation liquid dissolvesthe acids, volatile fatty acids, and other substances from the solidorganic waste bed. As a result, the percolation liquid is enriched witheasily digestible substances.

From the process tanks 5, excess percolation liquid is pumped via pumps8 into filter tanks 6 having an appropriate filling level. The filtertanks 6 are equipped with a coarse filter where bigger pieces (e.g.,large solids) can be separated from the liquid stream.

From there, the percolation liquid is pumped in a gas-tight manner intoa biogas reactor 9 by means of pumps 8. The biogas reactor 9 functionsaccording to a reaction principle that is common for wastewatertechnology (e.g., UASB, CSTR, sludge bed, solid bed reactor). Inside thebiogas reactor 9, the percolation liquid is digested rapidly intoexiting biogas 13, containing mainly CH₄ and CO₂. The degassedpercolation liquid is discharged from the biogas reactor 9 and returnedto the process tanks 5 using pumps 7.

FIG. 2 depicts an apparatus for composting solid waste, in accordancewith an embodiment of the invention. After the hydrolysis andmethanogenesis stages depicted in FIG. 1, the conditions in the processmodules 1 shifts from anaerobic (with percolation) to aerobic, as air isintroduced. In the depicted embodiment, air intakes 10 mounted on top ofthe process modules 1 are opened and pumps 11 start to draw aircontinuously or discontinuously (e.g., intermittently) through thealready percolated organic matter. After passing through the organicmatter, the air is discharged through a biofilter 12, where odors arescrubbed (e.g., using microorganisms) from the air.

FIG. 3 and FIG. 4 are analogous to FIG. 1 and FIG. 2, respectively, withminor changes in the process streams during thehydrolysis/methanogenesis stages (methanization process) depicted inFIG. 3. In FIG. 3, percolate that passes through the drain 3 at thebottom of a process module 1 first passes through a filter tank 6 priorto entry into the process tank 5. The filter tanks 6 are equipped with acoarse filter where bigger pieces (e.g., large solids) can be separatedfrom the liquid stream. Degassed percolation liquid from the biogasreactor tank 9 is also discharged to the process tanks 5, e.g., usingpumps. Thus, the process tanks 5 collect percolate from the processmodules 1 as well as liquid recycled from the biogas reactor tank 9, asdepicted in FIG. 3. Liquid from a process tank 5 is pumped to a sprayingsystem 2 in one or more process modules 1 (FIG. 3 depicts one processtank 5 per process module 1, but alternative embodiments may havemultiple process modules 1 sharing a single process tank 5). Thespraying system 2 continuously or discontinuously sprays the liquid overthe organic matter in the process modules 1 by means of pumps 4. FIG. 3depicts two process modules 1—each with associated process tank 5 andfilter tank 6—for every biogas reactor tank 9. However, there may bemany process modules 1 for a given biogas reactor tank 9. For example,in various embodiments, a plant may have at least 5, 10, 15, or 20process modules 1 for a given biogas reactor tank 9.

After the hydrolysis and methanogenesis stage depicted in FIG. 3, theconditions in the process modules 1 shifts from anaerobic to aerobic, asair is introduced. FIG. 4 depicts this aerobic composting stage, wherethe same process modules 1 through which percolate flowed in thehydrolysis/methanogenesis stage are used for aerobic treatment of theorganic waste, thereby obviating transport of the solids to anothervessel. In the depicted embodiment, air intakes 10 mounted on top of theprocess modules 1, as shown in FIG. 4, are opened and pumps 11 start todraw air continuously or discontinuously (e.g., intermittently) throughthe already percolated organic matter. After passing through the organicmatter, the air is discharged through a biofilter 12, where odors arescrubbed (e.g., using microorganisms) from the air.

EXEMPLARY EMBODIMENT

An example implementation of the system depicted in FIG. 3 and FIG. 3 isdescribed in this section. In this example, the system produces biogasby anaerobic digestion of solid waste material (e.g., municipal waste)over a period lasting from one to four weeks. The de-gasified materialis then decomposed through aerobic decomposition into a rich black soil,a process which takes an additional two to four weeks. The system allowscontrol of the biological processes while avoiding over-engineering ofthe technical facilities.

The municipal waste is weighed and registered, after which it isunloaded in a reception area where the quality and pureness of thematerial is assessed. Surface fluid from the reception area is ledthrough an oil separator and a sand collector to a receiving tank, thenpumped to sewer.

The solid municipal waste is then handled and pre-treated using mobileequipment such as front loaders, feed mixers and drum screens.Non-organic components such as plastic, metal, and the like areseparated out for incineration. The remaining waste is treated in a drumscreen filter. The filtered-out fraction is transported to incinerationwhile the ‘clean’ fraction is mixed with structure material such as woodbranches and rough garden waste in a feed mixer. In this example,approximately 2 kg of structure material is used for every 10 kg ofwaste. The mixed material is front loaded into the process modules 1.When full, each module 1 is closed by bolting the gas tight door shut.

Biogas is produced in two phases—hydrolysis and methanogenesis.Hydrolysis takes place in the process modules 1, e.g., 600 m³ concreteboxes or vessels, where each module 1 is fitted with sprinklers 2 andventilations systems 10. The organic waste in the closed process moduleis irrigated with percolate from the process tank 5. This percolationdraws out the fatty acids from the waste and the acidic percolate isthen used for gas production in the reactor tank 9. The hydrolysis inthe process module 1 runs for a period from two to four weeks.

Methane is produced in a gas tight reactor tank 9 (e.g., 1,500 m³membrane-covered concrete container), which is also used for gasstorage. The fluids (percolate) from the hydrolysis in the processmodules 1 are led to the reactor tank 9 where they feed themethanogenesis. Addition of percolate is controlled by the pH value inthe reactor tank. The pH in the tank should be from about 7 to about 7.5for good gas production. The process in the reactor tank 9 may takeplace without stirring, or with only light stirring. The reactor tank 9design may simply be a modification of bio-gasification tanks used forlivestock manure on farms.

The two processes—hydrolysis and methanogenesis—are thus handled inphysically separate containers, and the interface between the twocontainers is a separate process tank 5 (e.g., a 6 m³ vessel). Processcontrol is performed in the process tank 5 and all relatedinstallations, including valves, pumps, fans, and the like, can beestablished in or around the process tank. This allows there to be noelectrical installations in the process modules 1 or the reactor tank 9.In preferred embodiments, there is one process tank 5 connected to eachprocess module 1. A plant that employs this system may have, forexample, twenty process modules 1, each with a corresponding processtank 5, placed next to or opposite each other, and two reactor tanks 9,thus, in this example, 5 process modules 1 for every biogas reactor tank9.

From the reactor tank 9, the biogas can be led to a biogas motor thatproduces electricity supplied to the electricity grid and heat which isused internally in the system. The internal heating system can transferheat from the biogas motor to the reactor 9, offices, etc.Alternatively, the biogas can be captured and upgraded to higher methanecontent and fed to a natural gas system. A gas control unit measures gasflow and quality in the gas pipes, expressed by methane content, CO₂content, and O₂ content. In addition to methane, CO₂ may be captured aswell. The plant may be equipped with an emergency gas exploitation unit(e.g., gas flare) to exploit gas in the event of a biogas motorbreakdown or during repair.

Once the hydrolysis is complete, pathogenic microorganisms are removedfrom the material in a sanitation step where the temperature in theprocess module is raised to a minimum of 70° C. and for a minimum of onehour. After purification, the waste in the process modules 1 can beconverted to compost in the composting stage.

The composting process, depicted in FIG. 4, is activated by forcedaeration of the now de-gasified waste, at which time composting beginsand pH rises. The aeration may be performed by opening a pneumaticcontrolled damper 10 in the roof of the process module 1, therebyallowing atmospheric air into the module 1. Each process module 1 hasits own air intake 10. The air is sucked out through the drainage bottom3 via canals in the floor of the process module 1 using a fan placedoutside the process module 1.

Composting will generally run for two to four weeks in the processmodule 1, after which the compost is stable and can be moved to opencuring boxes for final composting without odor problems. The ventilationsystem transports air through the compost mass and sucks out process airto an air cleaning system 12. Process air cleaning is used to break downand clean odor components, such as ammonia. The air may be cleaned in asimple open surface biofilter or, if required, it can be wasted in ascrubber and subsequently cleaned in a biofilter. If the plant isequipped with a scrubber, then a water recycling system may beestablished to minimize water use.

FIG. 5 is a schematic drawing of views of an exemplary dual-purposedrain assembly 3 for transport of percolate from a process module 1during a digestion stage as well as for ventilation of the processmodule 1 during a composting stage. The exemplary dimensions shown arein millimeters. Reference 200 is a bottom view of a rail 201, withfunnels 202 through which percolate runs from the module (side A) to apipe 204 (side B) during the digestion stage (hydrolysis/methanogenesis)and through which air flows from the pipe 204 (side B) to the module(side A). The funnels 202 have a conical shape, with the narrow end 204facing the process module 1 and the wide end 206 facing the pipe 204.This design has been found to help prevent clogging of the funnel 202with biomass in the process module 1. In certain embodiments, the ratioof the diameter at the narrow end 204 to the diameter at the wide end206 is about 0.75. In certain embodiments, the ratio is no greater thanabout 0.90.

Reference 208 is a side view of a rail 201 from the process module 1side (side A), showing the narrow end 204 of the funnels 202. Reference210 is a side view of the rail 201 from the pipe side (side B), showingthe wide end 206 of the funnels 202. Reference 212 is a ground view ofthe rail 201 showing pre-fabricated shelves 214 which hold a steel plate216, and reference 218 is a ground view of the rail 201 showingpre-fabricated screw holes 220 for screws 221 that bolt the rail 201 tothe concrete 222.

Reference 224 is a top view of the rail 201. This view shows thepre-fabricated screw holes 220 for the screws 221 that bolt the rail 201to the concrete 222, and the prefabricated shelf 214 that holds thesteel plate 216. Dotted lines represent the funnels 202 described above.

Reference 230 is a ground view of the drainage system. Rails 201 are oneither side of a pipe 204. The rail may be made from polyethylene PEHDLF 1000, for example. Funnels 202 are drilled through the rails 201 toallow liquid percolate to flow from the process module 1 to the pipe 204during the hydrolysis stage, and to allow flow of air from the pipe 204to the process module 1 during the composting stage. A screw 221 boltsthe rail 201 directly into the concrete 222.

Percolate flows from the process module 1 into the pipe 204, and fromthere is transported to the filter tank 6, process tank 5, and thenbiogas reactor tank 9 during the hydrolysis/methanogenesis stage.Furthermore, during the composting stage, air flows through the pipe 204and into the process module 1 via the funnels 202. A steel plate 216(e.g., 6 mm-thick stainless steel) tops the pipe 204 and compost lies ontop of the steel plate 216. The steel plate 216 prevents compost/wastein the process module 1 from falling directly into the pipe 204. Theplate 216 is held in place by a shelf 214 fabricated into the rails 201.The shelf 214 allows the plate 216 to be easily removed for cleaning ofthe pipe 204 when composting is complete and the solid material has beenremoved from the process module 1.

EQUIVALENTS

While the invention has been particularly shown and described withreference to specific preferred embodiments, it should be understood bythose skilled in the art that various changes in form and detail may bemade therein without departing from the spirit and scope of theinvention as defined by the appended claims.

What is claimed is:
 1. An apparatus for decomposition of organic matterinto biogas and compost, the system comprising: a waste processing tankinto which solid organic waste is loaded and in which hydrolysis andcomposting takes place at separate times, with composting of the solidorganic waste taking place during a separate stage after hydrolysis iscompleted, wherein the waste processing tank comprises a drain at ornear its base, the drain allowing flow of the percolation liquid out ofthe waste processing tank during the hydrolysis stage, the drain alsoserving as a vent through which air flows into and/or out of the solidorganic waste in the waste processing tank during the composting stage;a controller programmed to automate addition of percolation liquid inthe waste processing tank and initiate switchover from hydrolysis tocomposting according to pH in the waste processing tank; a sprayingsystem configured to spray percolate liquid onto the solid organic wastein the waste processing tank during the hydrolysis stage, wherein thepercolate liquid comprises fatty acids leached from the solid organicwaste and wherein the percolate liquid is recycled from the base of thewaste processing tank during the hydrolysis stage; and a biogas reactortank into which the percolate liquid from the waste processing tank ispumped for generation of biogas under anaerobic conditions during agasification stage.
 2. The apparatus of claim 1, wherein the wasteprocessing tank is configured to operate at ambient pressure during thehydrolysis stage, the composting stage, or both.
 3. The apparatus ofclaim 1, wherein the waste processing tank is configured to operateunder anaerobic conditions during the hydrolysis stage.
 4. The apparatusof claim 1, further comprising a biofilter through which air from thewaste processing tank passes prior to discharge to the atmosphere duringthe composting stage.
 5. The apparatus of claim 1, further comprising afilter configured to separate solids from the percolate liquid.
 6. Theapparatus of claim 1, comprising at least two waste processing tanksconnected in parallel.
 7. The apparatus of claim 1, wherein the wasteprocessing tank comprises an acid-resistant lining or coating.
 8. Theapparatus of claim 1, wherein the biogas reactor tank is gastight. 9.The apparatus of claim 1, further comprising a heater for heating thepercolate liquid either in the biogas reactor tank or outside the biogasreactor tank.
 10. The apparatus of claim 1, wherein the biogas reactortank comprises a sump to separate sediment and/or particles from thepercolate liquid.
 11. The apparatus of claim 1, further comprising aliquid process tank into which percolate liquid from either the biogasreactor tank, the waste processing tank, or both flows prior to beingpumped to the spraying system for spraying onto the solid organic wastein the waste processing tank during the hydrolysis stage.
 12. Theapparatus of claim 11, wherein percolate liquid from both the biogasreactor tank and the waste processing tank flows into the liquid processtank prior to being pumped to the spraying system for spraying onto thesolid organic waste in the waste processing tank during the hydrolysisstage.
 13. The apparatus of claim 12, further comprising a filter tankconfigured to separate solids from the percolate liquid before thepercolate liquid enters the liquid process tank.
 14. The apparatus ofclaim 11, comprising one liquid process tank for every waste processingtank.
 15. The apparatus of claim 14, comprising at least five wasteprocessing tanks for each of one or more biogas reactor tanks.